QMP: add snapshot-blkdev-sync command

Add QMP bits for snapshot_blkdev command. This is the same as
snapshot_blkdev in the human monitor. The command is synchronous.

In the future async commands and or a break down of the functionality
into multiple commands might be added.

Also change the 'snapshot_file' argument to 'snapshot-file' in
the human monitor, so that it matches QMP.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@gmail.com>
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 92c5c3a..5d44edf 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -694,6 +694,40 @@
 EQMP
 
     {
+        .name       = "blockdev-snapshot-sync",
+        .args_type  = "device:B,snapshot-file:s?,format:s?",
+        .params     = "device [new-image-file] [format]",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_snapshot_blkdev,
+    },
+
+SQMP
+blockdev-snapshot-sync
+----------------------
+
+Synchronous snapshot of a block device. snapshot-file specifies the
+target of the new image. If the file exists, or if it is a device, the
+snapshot will be created in the existing file/device. If does not
+exist, a new file will be created. format specifies the format of the
+snapshot image, default is qcow2.
+
+Arguments:
+
+- "device": device name to snapshot (json-string)
+- "snapshot-file": name of new image file (json-string)
+- "format": format of new image (json-string, optional)
+
+Example:
+
+-> { "execute": "blockdev-snapshot", "arguments": { "device": "ide-hd0",
+                                                    "snapshot-file":
+                                                    "/some/place/my-image",
+                                                    "format": "qcow2" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "balloon",
         .args_type  = "value:M",
         .params     = "target",